Vacuum evaporation crucible



Oct. 5, 1965 w. LIBEN 3,210,525

VACUUM EVAPORATION CRUCIBLE Filed Dec. 24, 1965 75 Vacuum 2 PUMP u r I f /4 x 9 70 Saunas 0F HEflT/NG CuR/e E/VT INVENTOR WILL MM Z IB N BY MWWZZMK ATTORNEY United States Patent ""ce 3,210,525 VACUUM EVAPORATIQN CRUCIBLE William Liben, 11404 Monticello Ave., Silver Spring, Md. Filed Dec. 24, 1963, Ser. No. 333,067 9 Claims. (Cl. 219-271) This invention relates to apparatus for vaporizing coating materials in vacuum, and more particularly to an electrically heated vacuum evaporation crucible for use in making thin films of material for use in optical systems, control of radiation emission and absorption, in the fabrication of micro-electronic systems, and for similar applications.

A main object of the invention is to provide a novel and improved vacuum evaporation crucible which is simple in construction, which is economical in operation, and wherein the utilization efliciency of the emitted vapor stream is high.

A further object of the invention is to provide an improved electrical vacuum evaporation crucible which is inexpensive to fabricate, which is compact in size, and which requires a relatively small time to stabilize to operating temperature.

A still further object of the invention is to provide an improved electrical vacuum evaporation crucible which acts as its own heating element, which is durable in construction, and which is provided with means to produce become apparent from the following description and claims, and from the accompanying drawings, wherein:

FIGURE 1 is a partly diagrammatic vertical crosssectional view taken through a vacuum vaporizing apparatus employing an improved evaporation crucible constructed in accordance with the present invention.

FIGURE 2 is a horizontal cross-sectional View taken substantially on line 22 of FIGURE 1.

FIGURE 3 is an enlarged transverse cross-sectional view taken substantially on line 3-3 of FIGURE 1.

FIGURE 4 is an elevational view, partly in vertical cross-section, showing a modified form of evaporation crucible constructed in accordance with the present invention.

A method commonly employed for making thin films of vaporized metal or other evaporated materials for use in optical systems, control of radiation emission and absorption, in the fabrication of micro-electronic systems, and for similar applications, is to evaporate the material from a crucible maintained at a high temperature in a vacuum. A prime purpose of the present invention is to provide an improved evaporation crucible for use in this method.

Referring to the drawings, 11 diagrammatically designates a vacuum chamber in which is supported a body 12, such as a flat substrate, on the bottom surface of which it is desired to deposit a thin film of vaporizable material 13. Supported in any suitable manner a substantial distance below the body 12, for example, by its connecting wires 14 and 15, is a crucible 16 constructed in accordance with the present invention. The crucible 16 comprises a length of conductive metal tubing pinched flat at both ends, as shown at 17 and 18, the respective supply wires 14 and being connected to the flat ends in any suitable manner to provide a rigid mechanical joint, as by being welded or bolted thereto. The flat ends 17 and 18 thus serve as integral electrodes for the introduction of the current which heats the crucible to the desired evaporation temperature.

The tubular body 16 is centrally formed at its bottom 3,213,525 Patented Oct. 5, 1965 wall portion with an upstanding annular collar or projection 19, and rigidly secured on the top rim of this collar 19 is a flat disc 20 which has a diameter substantially greater than that of the collar, so that it projects circumferentially therefrom and defines an annular shielded space therebelow in which the material 13 to be vaporized is received, as shown. The shield disc 20 acts to prevent solid particles of material 13 suddenly ejected from the main mass thereof from being propelled directly toward the substrate member 12.

The top wall portion of tube 16 is formed above the shield disc 20 with a depending elfusant tube 21 of substantial length, projecting down into the crucible toward the disc 20. The cross-section of the efl'usant tube 21 is divided into a number of parallel vapor flow channels by the provision of partition plates 22 mounted in the tube parallel to its axis and being coextensive in length therewith, the ratio of the length to the cross-sectional areas of the vapor flow channels thus defined being relatively large.

If the tube 21 were omitted and merely a hole was provided for the vapor leaving the crucible, the discharging vapor would cover a relatively wide solid angle, with very little beaming in the forward direction (toward the substrate member 12). Since the substrate subtends only a relatively small solid angle at the effusant opening, only a small part of the total vapor stream would impinge on the substrate member under these conditions.

By employing the guide tube 21 and the partitions 22 therein defining relatively elongated narrow channels directed toward the substrate member 12, the vapor stream is beamed toward the substrate member and is confined within a relatively narrow solid angle, thereby providing very high deposition efliciency.

A channel-shaped reflector 23 is preferably provided beneath the crucible, as shown, to minimize radiation losses and to thereby minimize the electrical power required to maintain the crucible 16 at its required vaporization temperature.

Since the crucible mass is relatively small, the time required for the crucible temperature to stabilize to its operating value is small, and the thermal time constant thereof is relatively small.

The volume of the entire crucible is small since the crucible acts as its own heating element.

The elfiux of solid particles of the material 13 toward the substrate is controlled and minimized by the presence of the guard disc 20. The utilization eificiency of the vapor stream from the eftusant guide tube 21 is high, as well as the utilization efiiciency of the heating power.

In the form of the invention shown in FIGURE 4, a pair of radiation-reflective discs 24, 24, preferably of the same material as the tube 16, are secured in the intermediate portion of the tube 16, spaced symmetrically on opposite sides of the collar 19 and shield disc 20, and acting to reflect radiation inwardly toward the center of the crucible. The reflective discs 24 provide substantially increased heating efliciency and further minimize the electrical power required to maintain the material 13 at its required vaporization temperature, by reducing the radiation losses through the opposite end portions of the crucible.

While certain specific embodiments of a vacuum evaporation crucible have been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

What is claimed is:

1. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom walls, means to connect the opposite ends of the body to a source of heating current, an upstanding projection on the bottom wall of said body defining a generally annular charge-receiving space therearound, said body having an elrusant vapor opening located in its top wall above said space, and a plate-like guard member in said body overlying said charge-receiving space and located between said effusant vapor opening and said space.

2. A vacuum evaporation crucible comprising a tubular conductive body having opposing longitudinal wall portions, means to connect opposite end portions of said tubular body to a source of heating current, an upstanding projection in said body on one of said longitudinal wall portions defining a generally annular charge-receiving space therearound, said body having an effu'sant vapor opening in the other longitudinal wall portion opposite said space, and a guard plate mounted in said body between said space and said opening and being of sufiicient size to prevent direct discharge of particles of solid material from said space through said opening.

3. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom walls, means to connect the opposite ends of the body to a source of heating current, an upstanding collar element on the bottom wall of said body defining a charge-receiving space therearound, said body having an effusant vapor opening located in its top wall above said space, and a plate-like guard member secured on said collar element and overlying said charge-receiving space, said guard member being of sufiicient size to prevent direct discharge of particles of solid material from said space through said opening.

4. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom walls, means to connect opposite end portions of said body to a source of heating current, the bottom wall of said body being formed with an upstanding collar element defining a charge-receiving space therearound, the top wall of said body having an efiusant vapor opening located opposite said collar element, and a shield disc secured on said collar element, said disc being substantially greater in diameter than said collar element so as to circumferentially overlay said charge-receiving space and being sufiiciently large to prevent direct discharge of particles of solid material from said space through said opening.

5. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom walls, means to connect opposite end portions of the body to a source of heating current, means on the bottom wall of said body defining a charge-receiving space, said body having an effusant vapor opening in its top Wall and a vapor guide tube of substantial length depending from said opening toward said space, and a plate-like guard member in said body overlying said charge-receiving space and located between said guide tube and said space, the lower end of said guide tube being spaced above said guard member.

6. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom walls, means to connect opposite end portions of the body to a source of heating current, an upstanding collar element on the bottom wall of the body defining a charge-receiving space therearound, said body having an effusant vapor opening in its top wall and a vapor guide conduit of substantial length depending from said opening toward said collar element, and a disc member substantially greater in diameter than and rigidly secured on said collar element and circumferentially overlying said charge-receiving space, the lower end of said conduit being spaced from said disc member, said disc member being sufficiently large to prevent direct discharge of particles of solid material from said space through said conduit.

7. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom Walls, means to connect opposite end portions of the body to a source of heating current, an upstanding collar element on the bottom wall of the body defining a charge-receiving space therearound, said body having an eiiusant vapor opening in its top wall and a vapor guide conduit of substantial length depending from said opening toward said collar element, a disc member substantia ly greater in diameter than and rigidly secured on said collar element and circumferentially overlying said chargereceiving space, the lower end of said conduit being spaced from said disc member, said disc member being sui'ficiently large to prevent direct discharge of particles of solid material from said space through said conduit, and partition means secured longitudinally in and being substantially coextensive in length with said guide conduit, to define vapor guide channels having a relatively large ratio of length to cross-sectional area.

8. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom walls, means to connect the opposite ends of the body to a source of heating current, means on the bottom wall of said body defining a charge-receiving space, said body having an effusant vapor opening locate-d in its top wall above said space, a plate-like guard member in said body overlying said charge-receiving space and located between said effusant vapor opening and said space, and respective radiation-reflective members secured transversely in said body on opposite sides of and adjacent to said charge-receiving space.

9. A vacuum evaporation crucible comprising a substantially horizontal tubular conductive body having top and bottom walls, means to connect opposite end portions of the body to a source of heating current, an upstanding collar element on the bottom wall of the body defining a charge-receiving space therearound, said body having an effusant vapor opening in its top wall and a vapor'guide conduit of substantial length depending from said opening toward said collar element, a disc member substantially greater in diameter than and rigidly secured on said collar element and circumferentially overlying said charge-receiving space, the lower end of said conduit being spaced from said disc member, said disc member being sufliciently large to prevent direct discharge of particles of solid material from said space through said conduit, partition means secured longitudinally in and being substantially coextensive in length with said guide conduit, to define vapor guide channels having a relatively large ratio of length to cross-sectional area, and respective radiationreflective discs secured transversely in said body on opposite sides of and adjacent to said charge-receiving space.

References Cited by the Examiner UNITED STATES PATENTS 5/57 Shen et al ll849 6/60 Toohig ll849 

1. A VACUUM EVAPORATION CRUCIBLE COMPRISING A SUBSTANTIALLY HORIZONTAL TUBULAR CONDUCTIVE BODY HAVING TOP AND BOTTOM WALLS, MEANS TO CONNECT THE OPPOSITE ENDS OF THE BODY TO A SOURCE OF HEATING CURRENT, AN UPSTANDING PROJECTION ON THE BOTTOM WALL OF SAID BODY DEFINING A GENERALLY ANNULAR CHARGE-RECEVING SPACE THEREAROUND, SAID BODY HAVING AN EFFUSANT VAPOR OPENING LOCATED IN ITS TOP WALL ABOVE SAID SPACE, AND A PLATE-LIKE GUARD MEMBER IN SAID BODY OVERLYING SAID CHARGE-RECEIVING SPACE AND LOCATED BETWEEN SAID EFFUSANT VAPOR OPENING AND SAID SPACE. 